The objectives of this study are: (1) to separate by ultrafiltration and gel-filtration chromatography urniary proteins from stone forming, potential stone forming and non-stone forming patients; (2) to characterize separated urinary proteins for calcium binding activity, effect on seeded crystal growth and immunological reactivity to anti-stone matrix antibodies; (3) to search for some reliable urinary biochemical profile representative of stone forming and potential stone forming patients. The identification of specific urinary macromolecules and other biochemical parameters in the urine of stone forming patients will enhance our knowledge of the process of stone initiation and growth and may have practical application providing guidelines to prevent crystal-matrix aggregation. Twenty-hour urine specimens are collected from metabolically active non-infectious calcium oxalate/calcium phosphate stone forming patients and a non-stone forming control population. Urinary proteins of molecular weight 1,000-50,000 daltons are concentrated by ultrafiltration and separated by Sephadex column chromatography. Fractions are analyzed for calcium binding activity and effect on seeded crystal growth and immunologic reactivity to anti-stone matrix antibody. Initial investigations have revealed that low molecular weight urinary proteins (less than 35,000 daltons) are increased in stone formers when compared to the non-stone forming controls. Other biochemical differences between the 2 populations has been the finding of an increased incidence of heterozygous cystinuria in the stone forming population when compared to the non-stone forming controls. Further studies continue analyzing specific urinary proteins.